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Re: a little tune-up idea
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Posted by Nellie on May 23, 1999 at 05:01:48 from (199.190.126.66):
In Reply to: a little tune-up idea posted by RKS on May 21, 1999 at 20:12:36:
Very nice article and I'm going to try it, but it may work for different scientific reasons than you give.
The octane rating signifies anti-knock properties ONLY. The higher the octane rating the more anti-knock properties and the higher the cost. I don't know where these misconceptions about gasoline grades comes from, but let me assure you, all unleaded gasolines burn at the same temperature, regardless of octane rating. The only exception to this would be gasahol.
Gasoline octane numbers are adjusted by two methods: adding anti-knock compounds such as tetraethyl lead (now illegal in many states) OR using higher refining temperatures and pressures to reform the hydro- carbon molecules into more knock resistant compounds. Obviously, unleaded gas uses the second method, which is why unleaded gas costs more than leaded.
Let it be known to all, that regardless of the octane, there is more or less the SAME amount of energy (about 115,000 btu/gal) in gasoline grades. Octane numbers are adjusted by tweeking the proportion of about a hundred different hydrocarbon compounds that form gasoline. THIS ADJUSTMET DOES NOT EFFECT THE COBUSTION TEMPERATURE, JUST THE FUEL'S RESISTANCE TO KNOCK.
There IS a big difference in the blending of fuel depending on the climate and season. One of the big things they control is vapor pressure. This is to reduce hydrocarbon pollution from evaporation in the summer. Also, they add a lot of butane to the gas in winter to allow the engine to start.
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